The Interpretation of Dreams is a book by Sigmund Freud, the first edition of which was first published in German in November 1899 as Die Traumdeutung (though post-dated as 1900 by the publisher). The publication inaugurated the theory of Freudian dream analysis, which Freud believed was the "royal road to the unconscious".

At the beginning of Chapter One, Freud describes his work thus:

In the following pages, I shall demonstrate that there is a psychological technique which makes it possible to interpret dreams, and that on the application of this technique, every dream will reveal itself as a psychological structure, full of significance, and one which may be assigned to a specific place in the psychic activities of the waking state. Further, I shall endeavour to elucidate the processes which underlie the strangeness and obscurity of dreams, and to deduce from these processes the nature of the psychic forces whose conflict or co-operation is responsible for our dreams.

The book introduces the Ego, and describes Freud's theory of the unconscious with respect to dream interpretation. Dreams, in Freud's view, were all forms of "wish-fulfillment" — attempts by the unconscious to resolve a conflict of some sort, whether something recent or something from the recessess of the past (later in Beyond the Pleasure Principle, Freud would discuss dreams which did not appear to be wish-fulfillment). However, because the information in the unconscious is in an unruly and often disturbing form, a "censor" in the preconscious will not allow it to pass unaltered into the conscious. During dreams, the preconscious is more lax in this duty than in waking hours, but is still attentive: as such, the unconscious must distort and warp the meaning of its information to make it through the censorship. As such, images in dreams are often not what they appear to be, according to Freud, and need deeper interpretation if they are to inform on the structures of the unconscious.

Freud makes his argument by first reviewing previous scientific work on dream analysis, which he finds interesting but inadequate. He then describes a number of dreams which illustrate his theory. Many of his most important dreams are his own — his method is inanugerated with an analysis of his dream "Irma's injection" — but many also come from patient case studies. Much of Freud's sources for analysis are in literature, and the book is itself as much a self-conscious attempt at literary analysis as it is a psychological study. Freud here also first discusses what would later become the theory of the Oedipus complex.

The initial print run of the book was very low — it took many years to sell out the first 600 copies. Freud revised the book at least eight times, in the third edition added an extensive section which treated dream symbolism very literally, following the influence of Wilhelm Stekel. Later psychoanalysts have expressed frustration with this section, as it encouraged the notion that dream interpretation was a straightforward hunt for symbols of sex, penises, etc. (Example: "Steep inclines, ladders and stairs, and going up or down them, are symbolic representations of the sexual act.") These approaches have been largely abandoned in favor of more comprehensive methods[How to reference and link to summary or text].

Widely considered to be his most important contribution to psychology, Freud said of this work, "Insight such as this falls to one's lot but once in a lifetime."